Method for starting an engine

ABSTRACT

A method for improving starting of an engine that may be repeatedly stopped and started is presented. In one embodiment, the method disengages a starter in response to a first predicted combustion in a cylinder of the engine. The method may reduce one-way clutch degradation of a starter. Further, the method may reduce current consumption during engine starting.

FIELD

The present description relates to a system for improving starting of anengine. The method may be particularly useful for engines that are oftenstopped and then restarted.

BACKGROUND AND SUMMARY

Vehicle manufacturers have realized that it may be desirable under someconditions to automatically start and stop an engine of a vehicle.Stopping the engine can reduce fuel consumption, especially when thevehicle is stopped for longer periods of time, in stop-and-go trafficfor example. However, continuously stopping and starting an engine canincrease starter degradation, current consumption, engine noise andvibration, and starter one-way clutch degradation.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method for improving engine starting.

One embodiment of the present description includes a method for startingan engine, comprising: stopping the engine; predicting a firstcombustion cycle of a cylinder from engine stop in which an air-fuelmixture is combusted; engaging a starter; and disengaging said starterduring the predicted first combustion cycle.

Engine starting can be improved by disengaging a starter at apredetermined position that may be related to the first cylinder tocombust an air-fuel mixture since an engine stop. For example, a startercan engage the flywheel of an engine while the engine is stopped. Uponengagement of the starter to the flywheel, the starter can begin torotate the engine crankshaft and cause pistons within the cylinders toreciprocate. Crankshaft rotation causes valves that control flow throughcylinders to operate, and valve operation and piston movement may berelated such that they define or establish cycles of engine cylinders.And since cylinder cycles may be uniquely related to engine position, itmay be possible to predict in which cylinder a first combustion cyclewill take place. In particular, an engine controller can predict a firstcombustion event since engine stop in a cylinder based on engineposition and cylinder fueling data. Therefore, it is possible to predictwhen the engine will start so that a starter may be disengaged earlyduring an engine start.

The present description may provide several advantages. Specifically,the approach may reduce starter degradation, current consumption,overrunning clutch degradation, and engine noise/vibration. Further, themethod may provide these benefits without additional hardware.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings,wherein:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is an example plot of a simulated engine start sequence;

FIG. 3 is an example plot of an alternative engine start sequence; and

FIG. 4 is a flow chart of an engine starting routine.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57.

Intake manifold 44 is also shown coupled to the engine cylinder havingfuel injector 66 coupled thereto for delivering liquid fuel inproportion to the pulse width of signal FPW from controller 12. Fuel isdelivered to fuel injector 66 by a fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown). The engine 10 of FIG. 1is configured such that the fuel is injected directly into the enginecylinder, which is known to those skilled in the art as directinjection. Fuel injector 66 is supplied operating current from driver 68which responds to controller 12. In addition, intake manifold 44 isshown communicating with optional electronic throttle 64. In oneexample, a low pressure direct injection system may be used, where fuelpressure can be raised to approximately 20-30 bar. Alternatively, a highpressure, dual stage, fuel system may be used to generate higher fuelpressures.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 62. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. In a preferredaspect of the present description, engine position sensor 118 produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

In one embodiment, the stop/start crank position sensor has both zerospeed and bi-directional capability. In some applications abi-directional Hall sensor may be used, in others the magnets may bemounted to the target. Magnets may be placed on the target and the“missing tooth gap” can potentially be eliminated if the sensor iscapable of detecting a change in signal amplitude (e.g., use a strongeror weaker magnet to locate a specific position on the wheel). Further,using a bi-dir Hall sensor or equivalent, the engine position may bemaintained through shut-down, but during re-start alternative strategymay be used to assure that the engine is rotating in a forwarddirection.

Referring to FIG. 2, an example plot of a simulated engine startsequence by the method of FIG. 4 is shown. Time begins on the left sideof the plot and increases to the right side of the plot. The illustratedsequence represents a start of a non-limiting four cylinder four cycleengine. In this example, the vertical markers represent top-dead-centeror bottom-dead-center for the respective cylinder strokes. And, thereare 180° crankshaft degrees between each vertical marker.

The first plot from the top of the figure represents position ofcylinder number one. And, in particular, the stroke of cylinder numberone as the engine crankshaft is rotated. To the left of T₀, the engineis stopped or at rest. At T₀, the engine crankshaft begins to rotatefrom torque provided by a starter motor. Cylinder number one strokes arelabeled according to the engine position the engine assumed at enginestop. For example, cylinder number one was on an intake stroke at enginestop before time T₀. After T₀, the engine rotates and cylinder numberone enters the compression stroke followed by expansion and exhauststrokes. The cylinder cycle for cylinder number one then repeats. For afour stroke engine a cylinder cycle may be 720°, the same crankshaftinterval for a complete cycle of the engine. The star at label 200indicates the first ignition event for the first combustion event sinceengine stop. Star 208 represents the second combustion event forcylinder number one after engine stop and the fifth combustion eventsince engine stop. The ignition may be initiated by a spark plug. Inthis sequence, cylinder number one valves are open for at least aportion of the intake stroke to provide air to the cylinder. Fuel may beinjected the engine cylinders by port or direct injectors. The fuel andair mixture are compressed and ignited during the compression stroke.Peak cylinder pressure may occur at top-dead-center of compressionstroke or during the expansion stoke.

It should be noted that engine position may be determined at the time ofengine stop by tracking engine position as spark and fuel aredeactivated. In one embodiment, when the engine is substantiallystopped, engine position is determined and stored to memory forretrieval during the next engine start. In another embodiment, engineposition may be determined at engine start after the engine begins torotate by sensing camshaft and crankshaft positions.

The second cylinder position trace from the top of the figure representsthe position and stroke for cylinder number three. Since the combustionorder of this particular engine is 1-3-4-2, the second combustion eventfrom engine stop is initiated at 202 as indicated by the star. Star 202represents the initiation of the first combustion event for cylinderthree after engine stop and the second combustion event from the enginestop.

The third cylinder position trace from the top of the figure representsthe position and stroke for cylinder number four. Star 204 representsthe initiation of the first combustion event for cylinder number fourafter engine stop and the third combustion event from the engine stop.

The fourth cylinder position trace from the top of the figure representsthe position and stroke for cylinder number two. Star 206 represents theinitiation of the first combustion event for cylinder number two afterengine stop and the fourth combustion event from the engine stop.

It should be noted that the first cylinder to combust an air-fuelmixture can vary depending on the engine stopping position and themethod of determining engine position. In some embodiments fuel may notbe delivered to one or more engine cylinders until engine position isestablished. In other embodiments, fuel may be delivered before or assoon as the engine begins to rotate without regard to the enginestopping position.

The fourth plot from the top of the figure indicates control of starterengagement. During starter engagement, a solenoid moves a rotatingpinion gear from a position away from an engine flywheel to a positionwhere the pinion engages the flywheel and causes the engine crankshaftto rotate. In one embodiment, the pinion is initially rotated at a firstlow speed prior to engagement of the pinion to the flywheel. After thepinion engages the flywheel, the pinion speed is increased and thepinion remains engaged until the first cylinder predicted to combust anair-fuel mixture reaches a predetermined crankshaft position during thepredicted first combustion cycle. In one example, the pinion is engageduntil a crankshaft angle that corresponds to a position within theexpansion stroke of the first cylinder cycle in which the firstcombustion event is initiated. In the illustrated example, the firstcombustion since engine start is initiated at 200, and the starterpinion is disengaged from the fly wheel at 210 during the expansionstroke of cylinder number one. Shortly thereafter, the first combustionevent from engine stop is initiated.

In one example, the starter may be disengaged during the expansionstroke of the first cylinder to combust an air-fuel mixture and beforespark is delivered to another engine cylinder. In this way, the startercan be disengaged at different crankshaft angles depending on the numberof cylinders in the engine. For example, if spark advance for eachcylinder of a four cylinder engine is timed at 10 crankshaft degreesbefore top-dead-center compression stroke, a starter may be disengagedin the expansion stroke of the first cylinder to combust an air-fuelmixture up to 10 crankshaft degrees before bottom-dead-center expansionstroke of the first cylinder to combust an air-fuel mixture. In thissequence there is 170 crankshaft degrees between top-dead-centercompression stroke and when the starter is disengaged. On the otherhand, for a six-cylinder engine, the starter may be disengaged up to 70crankshaft degrees before bottom-dead-center expansion stroke of thefirst cylinder to combust an air-fuel mixture because the six-cylindertop-dead-center compression strokes are separated by 120 crankshaftdegrees, rather than 180 crankshaft degrees as may be the case for afour cylinder engine.

Returning to FIG. 2, the fifth plot from the top represents a starterpinion engagement during an engine start where the engine does notaccelerate as predicted. Before T₀, the engine is stopped and thecrankshaft is at rest. In response to a request to start the engine, thestarter pinion is rotated at a low speed and a solenoid engages therotating pinion to the crankshaft at T₀. Thereafter, the enginecrankshaft begins to rotate and the pinion speed is increased to asecond higher speed. The pinion remains engaged until 212 at which timeit is disengaged until 214 where it is reengaged. The pinion is againdisengaged at 216 and is reengaged at 218. Further, the pinion isdisengaged at 220 and is reengaged at 222. The starter is disengaged fora final time at 224. Each of the starter pinion engagements at 214, 218,and 222 correspond to engaging the engine flywheel with the starterpinion at a time before the next scheduled combustion event in theengine firing order. Each of the starter pinion disengagements at 216,220, and 224 correspond to disengaging the starter pinion during theexpansion stroke of the cylinder in which predicted combustion occurred.

The starter pinion is engaged and disengaged multiple times at 214-224.Further, the starter pinion may be reengaged in response to a number ofconditions. For example, the starter pinion may be reengaged if enginespeed does not reach a threshold or if a change in engine speed does notreach a threshold.

The starter pinion may be disengaged in response to a number ofconditions. For example, the starter pinion may be disengaged when thecrankshaft reaches a predetermined position corresponding to acrankshaft angle during the expansion or exhaust stroke of the cylinderin which combustion is predicted. In another example, the starter pinionmay be disengaged when engine speed exceeds a threshold or when theengine acceleration exceeds a threshold during the expansion or exhauststroke of the cylinder in which combustion is predicted.

In another example not shown, the starter may be initially engaged andthen disengaged after a predicted combustion event is expected to occur.In particular, the starter can be disengaged during the expansion orexhaust stroke of the first cylinder to combust an air-fuel mixtureafter an engine stop. If the engine does not accelerate as predicted,the starter can be reengaged until engine speed overruns the overrunningclutch of the starter. Thus, in this example, the starter pinion is notheld until a predetermined engine crankshaft angle. Rather, the starterpinion may be held engaged to the flywheel until the engine speedreaches a threshold.

Turning now to FIG. 3, an example plot of an alternative engine startsequence by the method of FIG. 4 is shown. Similar to FIG. 2, timebegins on the left side of the plot and increases to the right side ofthe plot. This illustrated sequence also represents a start of anon-limiting four cylinder four cycle engine. Again, the verticalmarkers represent top-dead-center or bottom-dead-center for therespective cylinder strokes, and there are 180° crankshaft degreesbetween each vertical marker.

The description of cylinder traces 1-4 is identical to that of FIG. 2,with the exception of combustion events. Therefore, for the sake ofbrevity, the description of FIG. 2 is carried over to FIG. 3 andrepetition of identical features is omitted. In FIG. 3 cylinder numbertwo is the first cylinder to combust an air-fuel mixture since enginestop. Combustion is initiated in cylinder number two by a spark at 300.The combustion event at 300 may occur earlier than the combustion eventat 302 (the first combustion event illustrated in FIG. 2) for severalreasons. In one example, cylinder number two captures air in thecylinder after exhausting gases and inducting air during an intakestroke while the engine is being stopped. In response to a request torestart the engine, fuel is directly injected into the cylinder andcombustion is initiated during the first compression stroke of cylindernumber two. In this way, the engine may be started with less crankshaftrotation.

In another example, cylinder number two may be started early when anair-fuel mixture is trapped in a cylinder during an engine stop. Forexample, an engine controller can deactivated fuel and spark in responseto an engine stop request and then briefly reactivate fuel when enginespeed is low so that an air-fuel mixture may be trapped in the cylinderwhen the engine is stopped. Then, in response to an engine startrequest, the starter can rotate the engine and a spark at 300 caninitiate combustion in cylinder number two so that cylinder number twomay be the first cylinder to combust an air-fuel mixture since enginestop.

In both the above examples, cylinder number two can be predicted as afirst combustion cycle of cylinder number two and as the first cylinderto combust an air-fuel mixture since engine stop. By controllinginjection timing so that fuel is injected to a cylinder on or advancingto a compression stroke, the first combustion event of a cylinder may bepredicted. In the example of Fig., cylinder number two is on itscompression stroke and is therefore the first engine cylinder predictedto combust an air-fuel mixture after an engine stop. In one example, thecompression stroke of cylinder number two is determinable from sensingcam and crankshaft positions at T₀ and as the engine rotates. In anotherexample, the engine stopping position may be retained in enginecontroller memory so that the engine position is known before an enginerestart is requested.

Thus, FIG. 3 differs from FIG. 2 in that cylinder number two is thefirst cylinder since engine stop to combust an air-fuel mixture. Sincecylinder number one is next in the firing order, it is the next cylinderto combust an air-fuel mixture at 302. Then, cylinder three combusts anair-fuel mixture at 304, cylinder number four combusts an air-fuelmixture at 306, and cylinder number two combusts an air-fuel mixture at308. Thus, in this starting sequence cylinder number two is the firstcylinder to combust an air-fuel mixture since engine stop, cylindernumber one is the second cylinder to combust an air-fuel mixture sinceengine stop, cylinder number three is the third cylinder to combust andair-fuel mixture since engine stop, and cylinder number four is thefourth cylinder to combust an air-fuel mixture since engine stop. Notethat combustion events 300-306 are the first combustion events fromengine stop in the respective cylinders. Therefore, combustion events300-306 are the first cylinder cycles for the respective cylinders inwhich the cylinders combust an air-fuel mixture.

Turning now to describe one starter control sequence illustrated as“STARTER SEQ. 1,” the sequence is based on the engine positionsillustrated by CYL 1-4 above the starter control sequence. The starterpinion may begin to rotate at a first low speed before T₀. At T₀, thestarter is moved to the engine flywheel and increases speed to a secondlevel. Since cylinder number two is in a compression stroke at enginestop, fuel is injected into cylinder two in response to an engine startrequest. Further, since cylinder number two is the first cylinder toreceive fuel and spark, it may be predicted that cylinder number twowill be the first cylinder to combust an air-fuel mixture since enginestop. As such, the engine controller disengages the starter pinion at312 during the expansion stroke of cylinder number two. In one example,the starter may be disengaged at a predetermined crankshaft position. Inanother example, the starter may be disengaged when engine speed orchange in engine speed exceeds a threshold during the first expansionstroke after the first combustion stroke after engine stop.

A second starter control sequence is illustrated as “STARTER SEQ. 2,”this starter control sequence is based on the cylinder positions aboveit, but during this sequence engine speed or acceleration does notexceed a threshold level until the starter pinion is finally disengagedat 326. The starter may begin to rotate at a first low speed before T₀.Since cylinder number two is in a compression stroke at engine stop,fuel is injected into cylinder two in response to an engine startrequest. As described above, cylinder number two is the first cylinderto receive fuel and spark, and it may be predicted that cylinder numbertwo will be the first cylinder to combust an air-fuel mixture sinceengine stop. The engine controller disengages the starter pinion at 314,during the expansion stroke of cylinder number two. The starter may bedisengaged at a predetermined crankshaft position. At 316, the starteris reengaged to the flywheel by controlling the starter pinion speed torotate near the engine speed and advancing the pinion to the engineflywheel. In one example, the starter is reengaged when engine speed oracceleration is less than a threshold level. The starter pinion isdisengaged at 318 after engine controller predicts that cylinder numberone is the second cylinder to combust an air-fuel mixture and after theengine crankshaft reaches a predetermined position in the expansionstroke of cylinder number one. The starter pinion is reengaged to theflywheel at 320 by controlling the starter pinion speed to rotate nearthe engine speed and advancing the pinion to the engine flywheel. Thestarter pinion is disengaged at 322 after the engine controller predictsthat cylinder number three is the third cylinder to combust an air-fuelmixture and after the engine crankshaft reaches a predetermined positionin the expansion stroke of cylinder number three. The starter pinion isreengaged to the flywheel at 324 by controlling the starter pinion speedto rotate near the engine speed and advancing the pinion to the engineflywheel. Finally, the starter pinion is disengaged at 326 after theengine controller predicts that cylinder number four is the fourthcylinder to combust an air-fuel mixture and after the engine crankshaftreaches a predetermined position in the expansion stroke of cylindernumber four. The starter is not reengaged because engine speed oracceleration has exceeded a threshold level. In this way, it is possibleto engage and disengage the starter pinion during an engine start sothat the starter may be disengaged early in a start sequence while atthe same time providing additional cranking torque if the engine doesnot start as expected.

Referring now to FIG. 4, a flow chart of an engine starting routine isshown. At 402, routine 400 judges whether or not an engine start requesthas been made. An engine start request may be made by an operator or bythe engine controller or by another system (e.g., a hybrid powertraincontroller). In one embodiment, the engine controller may retrieveengine position from memory. Engine position can be determined at enginestop by tracking engine position after fuel and spark have beendeactivated and until the crankshaft is at rest. For embodiments whereengine position may not be tracked or monitored during engine stop,engine position can be monitored by way of cam and crankshaft positionsensors after a request to start. If an engine start request is present,routine 400 proceeds to 404. Otherwise, routine 400 proceeds to exit.

At 404, routine 400 judges whether or not conditions are met for earlystarter disengagement. In one embodiment, if the ambient temperature isless than a threshold, the starter may be overrun by the engine beforethe starter pinion is disengaged. If ambient temperature is greater thanthe threshold, the starter can be disengaged during a cylinder cyclewhere it is predicted that the cylinder will combust a first air-fuelmixture since engine stop. Further, barometric pressure may be acondition by which a starter is controlled. For example, if barometricpressure is less than a threshold amount, the engine may be started andthe starter may not be disengaged until the engine overruns the starter.If barometric pressure is greater that a threshold the starter may bedisengaged during a cycle of a cylinder that is on a first combustioncycle since engine stop. If conditions for early starter disengagementare met, routine 400 proceeds to 406. Otherwise, routine 400 proceeds to426 where the starter remains engaged until engine speed overruns thestarter speed and engine speed exceeds a threshold. Thus, during a firstcondition the starter can be engaged to rotate the engine from stop anddisengaged when engine speed exceeds a threshold. During a secondcondition, different from the first condition, a first combustion cyclecan be predicted in which an air-fuel mixture is combusted and thestarter can be disengaged during the predicted first combustion cycle.

At 406, the starter pinion is commanded to a first low speed before thepinion is engaged to the engine flywheel. The low speed may reducestarter pinion and flywheel degradation. In an alternative embodiment,the starter may be engaged at cranking speed. The starter pinion speedmay be controlled by modulating the starter voltage or current. Afteradjusting the starter pinion speed, routine 400 proceeds to 408.

At 408, routine 400 engages the starter pinion to the flywheel. Thestarter pinion may be engaged to the flywheel by applying a voltage tothe starter engagement solenoid. After applying voltage to theengagement solenoid routine 400 proceeds to 410.

At 410, routine 400 judges whether or not the starter pinion has engagedthe engine flywheel. In one embodiment, a switch at the end of theengagement solenoid travel may indicate that the pinion has fullyengaged the flywheel. If the starter is engaged, routine 400 proceeds to412. Otherwise, routine 400 returns to 408.

At 412, routine 400 the starter pinion speed may be increased to asecond level to start the engine. For example, if the starter pinion isrotated at a first speed to reduce pinion and flywheel degradation, thestarter pinion speed can be increased after the starter is engaged toimprove engine starting. Routine 400 proceeds from 412 to 414 after anyadjustments to starter pinion speed are output.

At 414, engine position is tracked or monitored as the engine begins torotate. In embodiments where engine position is stored in memory atengine stop, engine position is revised as indication markers on the camand crankshaft pass engine position sensors. In embodiments where engineposition is not stored in memory at engine stop, engine position may beindeterminable until the engine rotates a small amount so that markerson the cam and crankshaft indicate a definitive engine position. Onceengine position is established, fuel can begin to be injected to enginecylinders. However, for embodiments where fuel and air are held in acylinder during engine stop, it can be predicted that the first cylinderto combust an air-fuel mixture will be the cylinder in which fuel wasinjected prior to engine stop. For example, if engine speed is low andthe engine controller injects fuel into cylinder number three because itis expected that the engine will stop during the compression stroke ofcylinder number three, it may be predicted that cylinder number threewill be the first cylinder after engine stop to combust an air-fuelmixture.

In one embodiment where an air-fuel mixture is not held in a cylinderduring engine stop, and where fuel is directly injected to a cylinder,fuel may be first injected to the first cylinder determined to be in acompression stroke if fuel injection can be completed before base sparktiming (e.g., base spark timing for a cylinder during a start may bebetween 10-20 crankshaft angle degrees before top-dead-centercompression stroke). If fuel cannot be injected before base sparktiming, fuel can be injected to the cylinder next in the order ofcombustion. In another embodiment where fuel is injected to a cylinderport, the first cylinder to receive fuel may be a cylinder that isdetermined to be on an intake stroke.

Once the engine controller establishes which cylinder is the firstcylinder to receive fuel since engine stop (e.g., by monitoring engineposition during an engine stop or by keeping track of which cylinder wasfirst to receive fuel after engine stop), the controller may predictthat the cylinder first to receive or hold an air-fuel mixture will bethe first cylinder to combust an air-fuel mixture. Likewise, first andsubsequent combustion of air-fuel mixtures since engine stop in othercylinders (e.g., the second cylinder to receive fuel since engine stop,the third cylinder to receive fuel since engine stop, and so-on) can bepredicted according to engine position and when fuel is injected to thecylinder. And, in a condition where the first predicted cylinder or asubsequent predicted cylinder does not accelerate the engine asexpected, the prediction of a first combustion cycle of a cylinder sinceengine stop advances according to the firing order of the engine. Forexample, if cylinder number one is predicted to be the first cylinder tocombust an air-fuel mixture after engine stop, but the engine does notreach a desired speed or accelerate as expected, then cylinder numberthree becomes the cylinder next predicted to be on its first combustioncycle. Likewise, other engine cylinders become the predicted cylinder tobe on their first combustion cycle as the engine continues to rotatethrough the engine cycle.

In one embodiment, the strokes of each cylinder may be stored in memoryand referenced to a 720 crankshaft degrees (e.g., the duration of acylinder cycle). For example, for a four cylinder engine,top-dead-center compression for cylinder number one may be referenced to0 and the expansion stroke identified as between 1 and 180 crankshaftdegrees. The exhaust stroke for cylinder number one may be between 181crankshaft degrees and 360 crankshaft degrees. The intake stroke forcylinder number one may be between 361 and 540 crankshaft degrees. Thecompression stroke for cylinder number one may be between 541 and 720 or0. The stroke of other engine cylinders may be likewise stored in memoryand referenced to the same 0 to 720 reference. Of course, the stroke ofother cylinders will be shifted with respect to the 720 degree window.For example, the crankshaft interval of the expansion stroke of cylindernumber one (1-180 degrees) corresponds to the compression stroke ofcylinder number three, the intake stroke of cylinder number four, andthe exhaust stroke of cylinder number two.

Thus, if engine position at start is first established as 200 degrees,it may be determined cylinder number one is in an exhaust stroke,cylinder number three is in an expansion stroke, cylinder number four isin an compression stroke, and cylinder number two is in a compressionstroke. Therefore, if fuel is first injected to cylinder number twobecause it is on a compression stroke, the engine controller can predictthat cylinder number two will be the first cylinder to combust anair-fuel mixture after engine stop. In this way, the first combustioncycle of a cylinder from engine stop in which an air-fuel mixture iscombusted may be predicted.

At 416, routine 400 judges whether or not the cylinder predicted tocombust and air-fuel mixture is at a predetermined crankshaft angle. Inone embodiment, the predetermined crankshaft angle may be a crankshaftangle in the expansion stroke of cylinder predicted to combust anair-fuel mixture. And, the particular angle may be an angle wherecrankshaft acceleration is expected to be highest. For example, thecrankshaft angle may be at or after the crankshaft angle where peakcylinder pressure is expected.

In one embodiment, the starter may be disengaged between 45 and 180degrees after top-dead-center of the compression stroke of the cylinderpredicted to combust an air-fuel mixture. In other words, the startermay be disengaged from 45 to 180 degrees into the expansion stroke ofthe cylinder predicted to combust an air-fuel mixture.

In another embodiment, the starter may be disengaged during the exhauststroke of the cylinder predicted to be in a first combust cycle. Bydisengaging the starter later in the cylinder cycle, the engine has anincreased opportunity to reach a desired engine speed or accelerationrate because other cylinders may combust air-fuel mixtures by the timethe crankshaft reaches the desired starter disengagement position.

It should be noted that other conditions and combinations of conditionsmay be combined to determine when the starter pinion is to bedisengaged. For example, if the engine rotates to the desired starterpinion disengagement crankshaft angle and the engine speed is below athreshold or has not accelerated as anticipated, the starter pinion mayremain engaged until the engine speed or acceleration is above thethreshold and a crankshaft angle to disengage the starter pinion of acylinder predicted to be in a first combustion cycle is reached.Further, the engine speed at which the starter may be disengaged may beincreased as altitude decreases or as barometric pressure increases.Further still, the engine speed at which the starter may be disengagedmay be decreased as altitude increase or as barometric pressuredecreases.

In one embodiment, during a stop/start re-start the first cylinder aircharge is calculated as a function of PV=mRT, or m=PV/(RT). Where P canbe measured with the MAP or Barometric sensor, as the MAP and cylinderair pressure quickly converge on the atmospheric pressure. T is thecylinder air temperature which is calibrated and calculated as afunction of engine coolant temperature. The volume is the trapped aircharge volume. If the first firing cylinder is positioned before intakevalve closure, IVC, then the volume is determined by the swept volumefrom IVC to TDC. If the particular engine has a VCT system with theability to accurately measure the intake CAM position then this can beused to estimate the first cylinder combustion torque as well. Thiswould also apply to the exhaust CAM position as advancing EVO reducesthe combustion energy transferred to the piston (e.g., the combustionforce/torque). If the first firing cylinder is located after IVC theinitial engine position will also affect the trapped air mass, and theresulting torque, which can be measured with the bi-directional Hall, orequivalent, crank position sensor.

If the engine has not reached the position at which the starter pinionmay be scheduled to be disengaged for the cylinder of the predictedfirst combustion cycle or if conditions have not been met to disengagethe starter, routine 400 moves to 414. Otherwise, routine 400 moves to418.

At 418, the starter is disengaged. The starter may be disengaged byremoving voltage from the starter engagement solenoid. In addition,current and voltage may be removed from the pinion motor so that thepinion coasts to a stop.

At 420, routine 400 determines whether or not the engine has started.The engine may be determined started when engine speed is greater than athreshold or when an acceleration rate of the engine exceeds a thresholdlevel. If the engine is determined to be started, routine 400 proceedsto exit. Otherwise, routine 400 proceeds to 422.

At 422, routine 400 rotates the starter pinion at a speed to matchengine speed. In one example, engine speed can be determined from acrankshaft position sensor and the starter motor can be supplied currentat a rate that corresponds to a rotational speed of the starter thatmatches the engine speed. For example, the present engine speed can beused to index a function that outputs starter motor current as afunction of starter speed. In this way, the starter motor current can besupplied to the starter in an open-loop manner such that starter motoror pinion speed does not need to be monitored. After the pinion speed isoutput, routine 400 proceeds to 424.

At 424, the starter is reengaged with the flywheel. In one example,voltage is applied to the starter solenoid at a predetermined crankshaftangle. For example, the starter pinion may be reengaged before the endof the exhaust stroke of the cylinder predicted to be on a firstcombustion cycle since engine stop. In another example, the starterpinion may be reengaged before the end of the expansion stroke of thecylinder predicted to be on a first combustion cycle since engine stop.In another example, the starter pinion may be engaged as soon as it isdetermined that the engine has not started.

Note that the engine position at which the starter is reengaged may bedifferent for different engines. The starter may be reengaged whenengine speed or acceleration is less than a threshold level by the timethe engine reaches a particular crankshaft position. For example, if theengine speed or acceleration does not increase above a threshold beforethe end of the expansion stroke of the cylinder predicted to combust anair-fuel mixture, the starter can be reengaged.

As will be appreciated by one of ordinary skill in the art, routinesdescribed in FIG. 4 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1-20. (canceled)
 21. An engine starting method, comprising: stopping theengine; predicting a first combustion cycle of a cylinder from enginestop in which an air-fuel mixture is combusted; engaging a starterbefore ignition of the air-fuel mixture; and disengaging the starterduring an expansion stroke of the predicted first combustion cycle. 22.The method of claim 21, wherein the starter is disengaged in response toengine acceleration exceeding a threshold.
 23. The method of claim 21,further comprising injecting fuel to an engine cylinder in response to arequest to start the engine.
 24. The method of claim 21, furthercomprising storing a stop position of the engine in memory of acontroller.
 25. The method of claim 21, further comprising starting theengine via a controller and disengaging the starter in response to peakcylinder pressure.
 26. The method of claim 21, wherein the engine isinstalled in a hybrid vehicle.
 27. The method of claim 21, wherein saiddisengaging of said starter is related to a speed threshold of saidengine.
 28. The method of claim 27, wherein said speed thresholddecreases as altitude increases and increases as altitude decreases. 29.The method of claim 21, wherein said starter is disengaged at apredetermined crankshaft angle during said cylinder cycle.
 30. A methodfor starting an engine, comprising: predicting a first combustion cycleof a cylinder from engine stop in which an air-fuel mixture iscombusted; starting the engine via engaging a starter; disengaging thestarter during the predicted first combustion cycle; and repeatedlyre-engaging the starter when a speed of the engine is less than athreshold.
 31. The method of claim 30, wherein starting the engine isinitiated by a controller.
 32. The method of claim 30, wherein a speedof a pinion of said starter is controlled to substantially match enginespeed during said re-engaging of said starter.
 33. A method of claim 30,further comprising disengaging and re-engaging the starter multipletimes with each re-engagement at a time before a next scheduledcombustion event in an engine firing order when speed does not reach thespeed threshold.
 34. The method of claim 30, wherein said speedthreshold increases as altitude decreases and decreases as altitudeincreases.
 35. The method of claim 30, further comprising disengagingsaid starter at a predetermined crankshaft angle during a cycle of asecond cylinder, said cycle of said second cylinder during a cylindercycle that said second cylinder is predicted to combust said air-fuelmixture.
 36. The method of claim 30, further comprising tracking engineposition via camshaft and crankshaft sensors.
 37. A method for startingan engine, comprising: during a first condition: engaging a starter torotate an engine from a stop and disengaging said starter when a speedof said engine exceeds a threshold, said starter being maintained asdisengaged; and during a second condition, different than said firstcondition: stopping the engine; predicting a first combustion cycle of acylinder from engine stop in which an air-fuel mixture is combusted;engaging a starter; and disengaging said starter during the predictedfirst combustion cycle.
 38. The method of claim 37, wherein during thesecond condition the engine is started via a controller request.
 39. Themethod of claim 38, wherein the engine is installed in a hybrid vehicle.40. The method of claim 37, wherein said starter is disengaged duringsaid second condition during an expansion stroke of the combustioncycle.